Electron flow device



Oct. 19, 1943. 2, J. ATLEE ET AL ELECTRON FLOW DEVICE Filed March 26,1942 w ww l lll -|Ill|ll Ill & Q9042. mrozzmsy Patented Oct. 19,1943 Igum-m STATES BA arl;

ELECTRON FLO QD l 1 Zed J.-Atlee, Elmhurst,lIll., and Robert'-F'.Wilson;

' Washingtom'D. C.,-assignors to General Eleca ,trici'X-Ray Corporation,Chicago,'Ill.,-a corpoii 1 p, rationof NewYork v V Application March2c,194g,'sena1N0.436,2so

7 y 3 Claims. romeo-27.5)

'The Present invention relates in general to electronics and hasmorelparticular referenceto improved electronic rectifier means.

An'important object of the invention isto pro vid'e' an electron flowdevice embodying an extremely efficient electron emission source; a furvther' object being to provide an. emission element adapted to be heated'for electron emission at relatively low temperature; astillfurtherobject being toutilize an emission element comprising thoriumforhighly efilcient electron emission.

' Another important object is toprovidean electron emision elementcomprising thorium supported on a suitable mountingpsuch as a tung stenfilament; a further object being to support the thorium as a surfacefilmonthe supporting filament. v

Another important object isto carbonize the tungsten filament whereby tocarry the thorium thereon in a sheath of tungsten carbide on said ameAnotherimportant object is-to provide an electron flow device embodyingthe improved elecing means to prevent endiproducts of the getteringoperation from settling upon the anode and cathode elements'oithedevicenThese andnumerous, other} portant objects,

* advantages, and inherent iun'ctions of the: inven tionwill be, fullyunderstood 'frjom'the following description, which,takenin'connectionwith the accompanying drawing, discloses a preferredembodiment of the invention.

' Referring to the drawing:]

Figure 1 is a sectional View t akenliongitudinally through an electronicrectifierembodying the invention, the'figure including a diagrammaticrepresentation of externalelectrical connections I for the operation ofthe rectifier; and

Figure 2 is a s ectionalview taken the drawing an electronic'devicecomprising a tron emission element asa cathode, inicornbi nationwith a co-operating anode, enclosed; in a sealed evacuated envelope, andto preserve the thorium by providingmeansformaintaining the exhaustedenvelope at a highdegree of vacuum of the order of 0.02 micron ofmercury or better;

a further object, to this end, being to provide l getteringmeans withinthe envelope and supported on a mounting preferably comprising a partofllthe cathode structure, ,said gettering means being operable toproduce agettering material such, as barium in vaporized condition atintervals during the service life of the device to maintain the desireddegree of'vacuum within the envelope for the preservation of theelectron rectifier ll, although the several featuresof the inventionarenot necessarilyliinited torectifiers I but may beutilized to advantage'generallyjin,

electronic devices embodying means forming an electron emitting source,

The rectifier ll,'as shown on" the drawing; may comprise'a sealedenvelope lt 'containing;

an anode l5 and a co-operating cathode 'll; "The envelope I3 may bevforniedof any suitablelen velope material and may be arranged inflariyconvenient or pr'eferred'iorm; As; shown, thejenvelope may comprise atublar gl as's'zshell' hav ing re-entrantnecks 19 at thefoppositeendsof theshell,the anode"lilandlcathode'l'l,being, 7

s respectively, supported on saidnecksat thefop emission element foroperation at'high efficiency. a c

Another important objectisto provide means withinthe envelope, operableas an ionization gaugaior the determination of vacuum conditions withinthe envelopejduring the operating life of the device; afurtheriobjectbeing to form the gauge as a plate havinga connectionextending outwardly of the:sealed-envelope for attachment in 'anexternal measuring circuitand oper- 4 able'as an ionic collector, saidplate servin in conjunction with the external measuring circuit,

, to measure the degree, of ionization andjhence,

, vacuum conditions within the envelope; a further object being to formthe ionization gauge plate as a part of the cathode structure'iofthedevice; a still further object being to utilizefthe' said gauge plate asa housing or enclosure for gettervelopethrough an opening formed thes'e'al,

" said",

preferably" comprises v an; electron emiss fila lament. A 7 The positeends of the envelope, The necks H! de-] fine openings which areclosedbyseal members-Ii 2i and 23of generally cup-shaped coniig' ra+'f tion.These members preferably comprise sheet metaLandeach has an annular rimwhich iormsf a glass-to-metal seal 25 with: the inwardly .fac f I neckis 'on which'the' seal merri berisfmounted to thuss'ealthe endoi t ingend of the velope.

JTheinernber 23,]at end of the'envelope, carries the anode i5, whichpreierablyfcomprisesj a; cup shaped element-formed with ajstem 25 whichprojectsoutwa'rdly'oi the1end'of theien;

member 23, the stem 26 being sealed opening. o j f 1 Thelmemberf'r I, atthe other end of velope, 'carries"thecathode llfwhich,'as shownp- I rsubs tan- H tially along the lines 25-2 in'Figurel'.

To illustrate the invention, thereis'shown on fitment n ethane solicitedin tungsten with the thorium component substantially uniformlydistributed in the filament. By operating the filament at hightemperature, the thorium is driven to the surface of. the filament toform a thorium film on, the surfaces of. the

filament. The heating of the filament to form a thorium film thereonneed not be accomplished until the filament has been assembled in theelectron flow device and may be' accomplished as a part of the processof conditioning the finished device for service. The process of thusconditioning the filament merely comprises the he'atingof the filamentto a temperature of the order of 2900 Kelvin; somewhat below the meltingtemperature of tungsten. v

A thoriate'd filament "oi the character herein described ischaracterized by the ability to' emit efiective electron quantities at'a temperature substantially lower than the effective operatingtemperature of a pure tungsten filament. Asa consequence, an electronflow device embodying a thoriated filament, in'accor'd'ance with theteachings of the present invention, is capable of functioning at alower' temperature 'and hence at appreciably higher efficiency with,substan tially longer life thanisi'the case with electron flow devicescontaining electron emission elements of the character heretoforeknowing In order to aid in holdingthe thorium on the filament during theserviee'liieoithe cathode and t6 therebymaintain the cathode as a highlyeflicient electron' 'source', itis desirableto car boniz'e the filamentin order toprovide a surface coating of carbide, specifically a tungstencarbide layer, where the filament comprises tungsten, since the thoriumhas a greater aflinity and'will be heldlnore securely on the filament bythe carbide tha'n'onfpure tungsten. iTo this end, the filamentispreferablycaiibonized by heating it to a temperature of the order of2,000 degrees centigrade in a hydrogen bottle or container in thepresence'of a carbonizing gas such as acetylene.

In this fashion, a sheath of tungsten carbide may be applied winesurface of thefilarnent to serve as a'foun'dation for holding thethorium on the filament. The carbonizing process Should be limited tothe surfaces and should not penetrate completely to the center of thefilament in order to avoid extreme brittleness, In performing thecarbonizing process, the degree of carbonization may bedetermined'bymeas'uring the electrical resistance of the filament fromtime totirnefthe resistance of tungsten carbide being substantiallyhigher than that of pure tungsten,.so thatadesired degree ofcarbonization may be readily determined by measuring the resistance ofthe 'filament being treated and by terminating carbonization when apredetermined resistancefhas been reached. f l

'The'cathode structure includes a disk-like head 43, preferably ofmetal, which head is mounted on a stud l5 extending in an opening formedin the seal member 2|, the stud being sealed in said opening andhavingportions extending outwardly or the envelope. Thehead ,43 carriesa tubular skirt 41 secured at one end on the head and extending at theother end in position enclosing the glass-to-metal seal 25. The skirtthus encloses a space 49 between the seal member 2| and the head 43,which space is in open communisurethe maintenance of a high degree ofvacuum within the envelope.

The cathode comprises the filament H which,

, at oneend, is mounted on, electrically connected to, andsupported by aconductor stem 21 which extends through: an opening 28 formed in thehead 43. The end of the stem 21 is mounted on the seal member-2| whichis formed with an opening fitted with a grommet 29 which receives thestem '21. The stem 21 is supported in and electrically insulated fromthe grommet and the seal member 2| by means of a globule of glass whichsupports the stem and seals the grommet opening around the stem.outwardly of the grommet, the stem 21 is electrically connected to aconductor 3|. The other end of the filament E1 is mechanically andelectrically connected on a mounting member comprising a wire 33 whichhas a hclically coiled portion 35 embracingthe filament and a supportingportion 31 which is supported on and electrically insulated from thehead 43 by means of a grommet 33 sealed in an opening in the head, thestem 31 being secured i electrically connected with the conductors 3|and 4| which extend outwardly of the envelope, such connection beingaccomplished by way of the stems 21 and 31 which are electricallyinsulated from the head 43.

It should be understood, of course, that an electron flow devicefunctions by the flow of electrons emitted at the cathode and travelingto and impinging'upon'the anode. When the flow device is constituted asa rectifier, the stream of electrons passing between the cathode andanode form a conduction path along which electrical current may flow inone direction only between the anode and cathode. This uni-directionalflow phenomena is utilized for the purpose of rectifying alternating orfluctuating electrical energy in order to provide uni-directionalelectrical power.

For efficient operation of the electron flow device, the atmospherewithin the envelope I3 is preferably maintained at pressures of theorder of 0.02 micron of mercury, and the maintenance of low vacuumconditions is of particular im-.

portance where the electron flow, device embodies x qfidi ervlce life,it is necessaryto reducethe possibility of ionic impact on the cathodefilament-and consequent dislodgment of thorium by eliminating, as faraspossible, the presenceof gaseous matter within the envelope.- To thisend,

means-is provided for insuring high vacuum conditions within .theenvelope throughout the serv-' ice life of the device. To this end, theenvelope is first thoroughly evacuated as apart of the' manufacture ofthe device, evacuation being acin the anode, cathode and envelope walls.After the devicehasthus been exhausted. to the greatest possibleexte'nt, theenvelope may be sealed off and as a final operation toremove all remaining impurities, a gettering operation isperformedwithinthe envelope. According to the present invention, gettering isaccomplished by vaporizing a suitable gettering materialwithin theenvelope, more particularly within the space 49. Barium may be utilizedas a gettering ma-. terial, and by vaporizing the same within the en- 63for regulating current flowjinthe'gettering circuit for getteringcontrol through-regulation of vaporization of the gettering material inthe chamber 49; It will be apparent, of course, that suificient'gettering materialmay be supplied within-the chamber 49 to enablesuccessive gettering operations to beperiormed within the envelope atintervals during theservice life of the device to thereby periodic'allyre-establishdesired operating life of the device.-

vacuum conditions within-the envelope 'inthe event that the'vacuum beimpaired during the The device of the present 'nventio'n also includesmeans for testing and measuring vacuum conditions within the envelopefrom time to time by ionization gauge means, including the head 43 andskirt 41 which, it will be noted, are elec- 'tri'cally connected onthestud 45 and otherwise insulated from the cathode and anode.

The degree of vacuum within the envelope I3 is a function of the numberof gaseous particles present within the envelope, and the number of suchparticles, in turn, is a function of the degree of ionization developedas a result of collision between electrons emitted by the cathode withany such gas particles present withinthe envelope. By measuring thedegree of ionization within the envelope resulting from a measurablevelope, all remaining impurities may be caused to unite with the bariumvapor to form innocuous i solid end pro-ducts which, upon condensationof the gettering material, will become deposited within the envelope is.=Byproviding a head 43 and the skirt ll, the end productswill bedeposited upon the internal surfaces-defining the get tering chamber 49.and thus will be prevented from depositing either upon the wall surfacesof the envelope I3 or upon working surfaces of the anode and cathode. I

Barium or other suitable gettering material may be supported within thechamber 49 and evaporated therein by any suitable or preferred means.Preferably, however, the gettering material is supported by a carrierwire 5| electrically connected at one end on the stud 45 and at theother end of a conductor 53, the carrier wire 5| having portionsintermediate the anchored ends thereof arranged in loops within thechamber 49. The conductor 53 extends through the seal member 2| and issealed, as by means of a globule of glass, in a grommet 59-similar tothe grommets 29 and 39 and, like them, sealed in the member 2|.outwardly of the envelope, the conductor 53 is electrically connected toa conductor 55.

The gettering material may be supported in any suitable or preferredfashion uponthe carrier wire 5|, which preferably is a hollow conductorwire enclosing the gettering material and having weakened wall portions.By passing electrical current through the wire 5|, as by connecting asuitable electrical power source 51 between the stud 45 and theconductor 55 outwardly of the envelope, the hollow carrier wire 5| maybe heated to thereby vaporize the gettering material carried by thewire, the material thus vaporized being projected outwardly of the wirethrough its weakened wall portions to perform the gettering operationwithin the chamber 49, resulting end products being deposited upon theinner walls of the head 43 and tubular skirt 41.

The gettering circuit between the stud 45 and the conductor 55, inaddition to the power source 51, preferably includes a meter 6| formeasuring current flow in the gettering circuit, an adjustable controlrheostat 65, and a control switch electron flow between cathodeandanode; it is possible accurately to determine the presence of gasparticles within the envelope and thereby determine the vacuum conditionat any time during the service life of the device. This maybeaccomplished by promoting a known electron flow between cathodev andanode and then measuring the resulting ionization by collectingresulting positive ions onthe head and skirt 43 and 41 andquantitatively measuring the ions thus collected. To this end, anionization gauge circuit comprising a meter 61 and a power source 69 maybe connected between either of the conductors 3 or 4| and the anode stem26, preferably under the control of a switch 1| and an adjustablecurrent flow regulating device, such as a rheostat 13. By adjusting therheostat, a known electron flow, as indicated by the meter 61, may beestab lished between the cathode and anode. I

By applying a negative bias to the head 43 and skirt 41 with respect tothe cathode H, as by means of a power source 15 connected between i oneof the cathode leads 3| or 4| and the stud 45which is electricallyconnected with the head 43 and the skirt 41, positive ions producedwithin the envelope will be caused to impinge upon the head 43 and skirt41, the extent of such ionic.

impingement being accurately measurable upon the meter 11 which isincluded with the power source 15 in the biasing circuit between thestud 45 and the cathode I1. Whenever the meter 11 shows ionization abovea predetermined minimum, it will be known that the desired vacuumcondition within the envelope |3 has been impaired and that the deviceshould be reconditioned by theperformanoe of a gettering operaf tion inorderto recondition the device for operation at maximum efiiciency,

It will be understood, of course, that the circuits shown in solidlines, namely, the ionization circuit including the meter 51, theionization measuring circuit including the meter 11, and the getteringcircuit including the meter 5!, are connected with the device in themanner shown only when it is desired to measurevacuum conditions withinthe envelope |3 and recondition the device by the performance of agettering operation. When the device; is in: service,- i tlmay beconnectedin any preferred rectifier system. For example, the'rectifiermay ordinari1y=be connected as indicated-in:dotted lines, illustrating;a filament transformer, 19 connected;to supply'filament current throughthe filament'conductors 3i and II and an alternating ,currentpower inputransformer: 8| connected between -.the;: anode a I 5 and cathode I1through aunidirectional @power outlet connections. a

It is thought that-the invention andits ;nu-

merous attendant advantages will berfully under-v stood from theforegoing description, and it is obvious that numerous changes may. bemade-in the form, construction and arrangement of the several :partswithout departing from :the spirit .or scope of the invention, orsacrificing any of its attendant advantages, the form herein disclosedhein'ga preferred embodiment for the purpose of illustrating-theinvention.

The invention is hereby claimed as-follows:

1. An electron flow devicecomprising asealed evacuated envelopecontaining an anode and a co-operating'ecathcde comprising gthorium on asuitable support, means forming an enclosuretin communication-with thespace; in said envelope,

arsupply of evaporablegettering. material in said enclosure,meansoperable'outwardlyof the envelope for the controlled evaporation ofsaid material withinsaid enclosure, said enclosureserving as acollectorin and on which the gettering materialmay condense afterevaporation tothus prevent condensation of. gettering material on theanode and cathode, saidgmeans forming-the enclosure comprisingelectrical conductingmaterial forming an: ionization gauge plate -intheenvelope and electrically insulated from said .anode and cathode, andmeans for connecting said plate in an ionization measurement circuitoutwardly of the envelope.

2. Anelectron flow device comprising a sealed evacuated envelopecontaining an anode and a "co-operating cathode comprising thorium on asuitable support, and means for measuring ionization within the envelopeto determine the evacuated condition therein comprising conductor.meansforming an ionization gauge plate in the envelope in position to collectpositively charged ions produced by electron flow between anodeandcathode, said plate being insulated from said anode and'cathode, andmeans for connecting the plate in an external electric circuit-for thequantitative measurement of ions collected thereon.

3. A high voltage, high vacuum electronic rec- -tifier comprising asealed evacuated envelope, an

able upon predetermined expansion of the material therein, and meansconnected with said enclosure and operable outwardly of said envelope tocause the material to expand within the enclosure to rupture saidwallportion and at intervals thereafter to evaporate the material in theenvelope to maintain high vacuum conditions within the envelope andthereby preserve the thorium in situ on the support means.

ZED J. ATLEE. ROBERT F. WILSON.

